1. Field of Invention
The present invention relates to a half-duplex method and apparatus for measuring a distance between two objects using RF techniques. More specifically, the present invention relates to a method and apparatus for maintaining phase lock between two wireless devices in a half-duplex distance measurement system.
2. Description of the Related Art
Mobile telephones, pagers, and other wireless communication equipment are now commonplace. More recently, laptop computers, personal digital assistants (PDAs)xe2x80x94such as the Palm(trademark) organizerxe2x80x94have been equipped with wireless communications capabilities. One of the primary benefits of wireless equipment is portability. We can carry our mobile phone with us wherever we go. These wireless devices are currently used for relatively limited purposes, such as making telephone calls, when they are capable of doing much more.
One potential use for wireless devices is in mobile commerce. Wireless devices can be used for buying or selling goods or services, making payments, gathering information, advertising and promotion, and the exchange of information for other commercial or non-commercial purposes. The success of mobile commerce and other wireless applications will depend on their acceptance by consumers at large. Accordingly, wireless applications must be easy to use and convenient. New platforms are being developed to enable mobile commerce and other applications for wireless devices. Bluetooth(trademark) is such a technology. Bluetooth(trademark) provides a wireless networking protocol for linking various wireless equipment, such as mobile computers, mobile phones, and PDAs. Bluetooth(trademark) operates in the Industrial Scientific and Medical (ISM) 2.4 GHz region.
In addition to platforms such as Bluetooth(trademark), wireless devices require additional enabling technologies to reach their full potential. One such technology involves distance measurement. The distance between two or more wireless devices may be needed in a variety of applications. In many cases, it may be undesirable to measure the distance between two wireless devices directly. Direct distance measurement may be impossible, impractical, intrusive, or simply inconvenient. Moreover, because one or more wireless devices may be moved, the distance between devices will not be fixed indefinitely and re-calculation may be needed.
In such situations, xe2x80x98wirelessxe2x80x99 distance measurements are used. Some xe2x80x98wirelessxe2x80x99 distance measurement systems require an infrastructure to be put in place such as GPS based systems, triangulation methods, and other positioning techniques. Other systems require line-of-sight conditions (e.g., infra red, laser, and optical methods). Radar as well as ultra sonic systems are bulky, complex, and consume significant amounts of power. New ultra wide band techniques are currently not approved by the authorities. Some less expensive systems offer solutions based on field strength measurements with the tradeoffs of reduced reliability and high environmental dependency.
The present invention has been made in view of the above circumstances and has an object to provide a system and method for accurately measuring distance using RF techniques. In one aspect of the invention there is provided a half-duplex wireless remote device for use in a distance measurement system, comprising a receiver for receiving a first radio frequency (RF) signal during a first time slot An from a wireless communication device, the first RF signal including a sequence of carriers fn, where n is a plurality of integers, wherein the sequence of carriers fn are phase coherent with a first reference signal generated at the wireless communication device, the receiver generating a second reference signal from the received first RF signal during the time slot An, wherein the second reference signal is phase coherent with the received first RF signal; a phase locked loop (PLL) for generating a third reference signal synchronized in frequency and phase with the second reference signal; a synthesizer for generating a second RF signal, the second RF signal being phase coherent with the third reference signal and including a sequence of carriers corresponding to the carriers fn of the first RF signal; and a transmitter for transmitting the second RF signal during a second time slot Bn, wherein the first time slot An and the second time slot Bn alternatingly repeat as n changes.
In another aspect of the invention, there is provided a method of phase locking a wireless communication device and a wireless remote device, comprising the steps of receiving a first radio frequency (RF) signal during a first time slot An from the wireless communication device, the first RF signal including a sequence of carriers fn, where n is a plurality of integers, wherein the sequence of carriers fn are phase coherent with a first reference signal generated at the wireless communication device, generating a second reference signal during the time slot An from the second reference signal, the second reference signal being phase coherent with the received first RF signal; generating a third reference signal synchronized in frequency and phase with the second reference signal; generating a second RF signal, the second RF signal being phase coherent with the third reference signal and including a sequence of carriers corresponding to the carriers fn of the first RF signal; and transmitting the second RF signal during a second time slot Bn, wherein the first time slot An and the second time slot Bn alternatingly repeat as n changes.
Additional objects and advantages of the invention will be set forth in part in the description that follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention will be realized by means of the elements and combinations particularly pointed out in the appended claims.
It should be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention as claimed. It will be apparent to those skilled in the art that various modifications and variation can be made without departing from the scope or spirit of the invention.